SCH3 U R.H. KING ACADEMY Chemical Bonding Worksheet Name: IONIC BONDING

Transcription

1 Chemical Bonding Worksheet IONIC BONDING 1. Draw the electron dot structures for the following atoms or ions:- (On a separate piece of paper) A. nitrogen atom B. nitride ion C. sodium atom D. sodium ion E. bromine atom F. oxide ion 2. Why do atoms become ions? List all reasons you can think of. Atoms become ions because: Atoms become more stable with a full valence shell of electrons, therefore an element is always seeking to gain or lose electrons in order to become stable! Certain elements can gain or lose electrons, becoming ions in order to reach noble gas configuration. 3. Define Ionic Bond: An ionic bond is the strong electrostatic force of attraction between oppositely charged ions formed due to transfer of electrons. A cation is formed by the loss of 1 or more electrons. An anion is formed by the gain of 1 or more electrons. 4. Draw the dot structures showing the transfer of electrons that occurs in the formation of the following ionic compounds and write the correct chemical formula: (On a separate piece of paper) A. Ca and P B. K and Si C. Ga and Cl D. aluminum oxide 5. What is the net charge on each of the above compounds? ZERO Why? Number of electrons lost= Number of electrons gained AW1

2 Complete the following Textbook questions. 6. P. 60 # 6,8; 6. The strong ionic bonds will keep ionic compounds in the solid state at ambient temperatures. When the ionic crystal structure is offset, this may result in ions with like charges being side by side, and consequently the repelling forces of like charges will shatter the compound. 8. (a) Element A with 2 valence electrons is most likely a metal. Element B with 7 valence electrons is a nonmetal. (b) Elements A and B would form a compound as follows: Two B atoms are needed for every A atom. (c) An ionic compound is formed. (d) The chemical formula for this compound is AB2. P. 90 # 55 (a) An ionic compound will form between elements C and D. With 1 valence electron, C must lie in column 1 of the periodic table. With 6 valence electrons, D must lie in column 16 of the periodic table. These columns lie relatively far apart, so the difference in electronegativity between C and D will likely exceed 1.7, particularly considering that C is metallic and D is nonmetallic. With a difference in electronegativity greater than 1.7, C and D will form an ionic bond. (b) C and D will combine as follows: (c) The chemical formula for the compound that will form is C 2 D. (d) C 2 D is a formula unit.

3 COVALENT BONDING Use Lewis diagrams to show the bonding in the following compounds: (On a separate piece of paper) PART 1 A. HCl B. H 2 O C. NH 3 D. PF 3 E. SCl 2 F. IBr G. I 2 H. PCl 3 I. AsH 3 J. AlCl 3 K. Cl 2 PART 2 A. CO 2 B. N 2 C. O 2 D. P 2 S 3 E. Ga 2 S 3 PART 3 A. C 2 H 6 B. C 2 H 4 C. C 2 H 2 D. CH 3 OH E. C 5 H 12 PART 4 Draw Lewis diagrams for each of the following compounds: Remember to include the resonance structure in applicable. A. SO 2 B. SO 3 2- C. SO 4 + D. NH 4 - E. NO 3 3- F. PO 4 2- G. SO 3 PART 5 A. XeF 4 B. PCl 5 C. IBr 3 D. ICl 5 E. ICl 7 F. XeF 2 G. XeF 6 H. BH 3

4 PART 6 Complete the following Textbook questions. P. 65 # 1 a; c; d; e; h; i; j: a) c) d) e) h) i) AW4

5 j) P. 67 # 2 a; b P. 69 # 2 b; d; g; i; j; n # 4 a; d 2 b) d) g) i) AW5

6 j) a) P. 89 #36 a; e; f; g; i e) f) g) i) P. 90 # 54,57,62, If an unknown solid compound has a high melting point, is hard and/or brittle, and conducts electricity in the liquid state, it is most likely ionic. If it has a low melting point, is soft or waxy, and does not conduct electricity, it is likely molecular. 57. (a) A Lewis structure that obeys the octet rule cannot be drawn for a nitrogen monoxide molecule because no matter how the electrons in a nitrogen monoxide molecule are arranged, 1 electron will remain unpaired in the Lewis structure, causing one of the atoms to have an odd number of electrons in its valence shell. For example: AW6

7 (b) The molecular structure of nitrogen monoxide accounts for its high reactivity and toxicity as follows: Since one of the atoms in a nitrogen monoxide molecule does not have an octet of electrons due to an unpaired electron, nitrogen monoxide molecules are unstable and, therefore, very reactive. The high reactivity would contribute to the toxicity of nitrogen monoxide. 62. A polyatomic ionic compound contains both ionic and covalent bonds. Sample answer: For example, sodium sulfate has ionic bonds between sodium cations and sulfate anions. However, it also has covalent bonds between the sulfur and oxygen atoms within the sulfate anion. 63. A beryllium atom has only 2 valence electrons, and each of these can join with an electron from another atom to form a bonding pair of electrons. For example, 1 beryllium atom can combine with 2 hydrogen atoms, and thus beryllium has a bonding capacity of two: Even though an oxygen atom has 6 valence electrons, it has only 2 unpaired electrons in its valence shell and can only form 2 single bonds to other atoms while obeying the octet rule. In a water molecule, for example, an oxygen atom combines with 2 hydrogen atoms: This illustrates that an oxygen atom has a bonding capacity of 2, just like a beryllium atom. AW7

8 POLAR COVALENT BONDING Complete the following Textbook questions. P. 73 # 4,5 (a-c),6 (a-b),8 (a-b) 4. A polar covalent bond is a covalent bond formed between atoms with significantly different electronegativities, thus resulting in a bond with localized positive and negative charges, or poles. A non-polar covalent bond is a covalent bond formed between atoms with identical (orvery similar) electronegativities. 5. Electronegativity difference and type of bond formed between two elements: (a) Ca S: ΔEN = 1.6, polar covalent (b) H F: ΔEN = 1.8, ionic (c) P H: ΔEN = 0, non-polar covalent 6. (a) H F is a more polar bond than H Cl. (b) O H is a more polar bond than C H. 8. (a) The most ionic bond possible between any two elements in the periodic table is Fr F, the bond that forms between an atom of francium, F, and an atom of fluorine, F. Fluorine has the highest electronegativity value of all the elements (4.0) and francium has the lowest (0.7), so the electronegativity difference between francium and fluorine (3.3) is the highest possible between two elements and thus Fr F is the strongest ionic bond. (b) A compound that contains the Fr F bond would exhibit strong ionic compound characteristics: it would have a very high melting point and boiling point, it would be soluble in water, and it would form an electrolyte. P. 92 # 66, A Pauling electronegativity value measures the tendency of an atom to pull a pair of electrons toward itself when bonded. Since helium, neon, and argon atoms do not bond to other atoms, Pauling electronegativities cannot be assigned to them. 70. Of nitrogen, N2(g), hydrogen fluoride, HF(g), and hydrogen bromide, HBr(g), hydrogen fluoride would have bonds with the greatest δ+ and δ charges. The δ+ and δ charges result from the electronegativity difference between the entities. The ΔEN values for the pairs of entities are: nitrogen, 0; hydrogen and fluoride, 1.8; and hydrogen and bromine, 0.8. The bond in HF(g) is the most polar, meaning HF(g) molecules would have the greatest δ+ and δ charges. AW8

9 P. 108 # From most polar to least polar: (a) K Br, H Br, O F, C H (b) C F, O H, C O, H H (a) O 2 is a symmetrical molecule because the two covalent bonds are arranged symmetrically between the two oxygen atoms. (b) H 2 O is an asymmetrical molecule because the covalent bonds are arranged asymmetrically about the oxygen atom. (c) CO 2 is a symmetrical molecule because the covalent bonds are arranged symmetrically about the central carbon atom. (d) CH 4 is a symmetrical molecule because the covalent bonds are arranged symmetrically about the central carbon atom. (e) NH 3 is an asymmetrical molecule because the covalent bonds are arranged asymmetrically around the nitrogen atom, with a lone pair on top. 5. (a) CCl 4 has one carbon atom and four chlorine atoms in each molecule. There are four covalent C Cl bonds.!en = ENCl ENC = 3.2 " 2.6 = 0.6 Therefore, each C Cl bond is polar covalent. The shape of the molecule is symmetrical. Also, the molecule is composed of carbon and four atoms of the same element. Therefore, CCl 4 is a non-polar molecule. (b) H 2 O has one oxygen atom and two hydrogen atoms in each molecule. AW9

10 There are two covalent O H bonds.!en = ENO ENH = 3.4 " 2.2 = 1.2 Therefore, each O H bond is polar covalent. The shape of the molecule is asymmetrical. Also, the molecule is composed of oxygen and two other atoms of the same element. Therefore, H 2 O is a polar molecule. (c) HF has one hydrogen atom and one fluorine atom in each molecule. There is one covalent H F bond.!en = ENF ENH = 4.0 " 2.2 = 1.8 The single H F bond is therefore polar covalent. A diatomic molecule made up of two different molecules is always polar. Therefore, HF is a polar molecule. (d) CFl 4 has one carbon atom and four fluorine atoms in each molecule. There are four covalent C F bonds.!en = ENF ENC = 4.0 " 2.6 = 1.4 Therefore, each C F bond is polar covalent. The shape of the molecule is symmetrical. Also, the molecule is composed of carbon and four atoms of the same element. Therefore, CF 4 is a non-polar molecule. AW10

11 (e) CH 3 Cl has one carbon atom, three hydrogen atoms, and one chlorine atom in each molecule. There are three covalent C Cl bonds and one covalent C H bond.!en = ENCl ENC = 3.2 " 2.6 = 0.6 and!en = ENC ENH = = 0.4 Therefore, each bond is polar covalent. The molecule has a positive side and a negative side. Also, it is asymmetrical, and it is made up of carbon and atoms of two other elements. Therefore, CH3Cl is a polar molecule. 6. Polar liquids will bend toward charged materials. Charged materials will not deflect non-polar liquids. Therefore, (a) Carbon tetrachloride, CCl 4 (l), is non-polar, because it was unaffected by the charged strips. (Also, it is a symmetrical molecule, and the chemical formula is carbon and one other element.) (b) Methanol, CH 3 OH(l), is polar, because the charged strips attracted it. (Also, it is an asymmetrical molecule, and the chemical formula is carbon and two other elements.) (c) Hexane, C 6 H 14 (l), is non-polar, because it was unaffected by the charged strips. (Also, it is a symmetrical molecule, and the chemical formula is carbon and one other element.) (d) Nitrogen trichloride, NCl 3 (l), is polar, because the charged strips attracted it. (Also, it is an asymmetrical molecule, and the chemical formula is nitrogen and three atoms of one other element.) AW11

12 INTER/INTRAMOLECULAR FORCES 1. Intramolecular are stronger. 2. A covalent bond is 100x stronger. 3. The molecules gather together as liquids or solids at low temperatures. 4. Based on boiling points, CH 4 (-162) has the weakest forces, H 2 O has the strongest (100). 5. London forces Are present in all compounds Can occur between atoms or molecules Are due to electron movement not to DEN Are transient in nature (dipole-dipole are more permanent). London forces are weaker 6. A) F 2 would be lower because it is smaller. Larger atoms/molecules can have their electron clouds more easily deformed and thus have stronger London attractions and higher melting/boiling points. B) O 2 because it has only London forces. NO has a small DEN, giving it small dipoles. 7. C 8 H 18 would have the higher melting/boiling point. This is a result of the many more sites available for London forces to form. 8. a large DEN, 2) the small sizes of atoms. 9. a) NH 3 : Hydrogen bonding (H + N), London. b) SF 6 : London only (it is symmetrical). c) PCl 3 : DEN= Dipole-dipole, London. d) LiCl: DEN= Ionic, (London). e) HBr: DEN= Dipole-dipole, London. f) CO 2 : London only (it is symmetrical) 10. Challenge: In ethanol, H and O are bonded (the large EN results in H-bonding). In dimethyl ether the O is bonded to C (a smaller EN results in a dipole-dipole attraction rather than hydrogen bonding). 11. Boiling points increase down a group (as period increases) for two reasons: 1) EN tends to increase and 2) size increases. A larger size means greater London forces. Boiling points are very high for H 2 O, HF, and NH 3 because these are hydrogen bonds (high EN), creating large intermolecular forces AW12

13 Complete the following Textbook questions. P.115 # 7 7. (a) Water has a considerably higher boiling point than methane, CH 4 (g), because of the strong hydrogen bonds between water molecules. Methane molecules only have the relatively weak London dispersion forces between them. (b) Bromine is a liquid at ordinary temperatures whereas chlorine is a gas because the London dispersion forces between Br2 molecules are stronger than the London dispersion forces between Cl 2 molecules. This is because as the size of the molecule increases there are more electrons and protons attracting each other. (c) Trichloromethane, CHCl 3, has a higher boiling point than tetrachloromethane, CCl 4, because trichloromethane is polar, with dipole dipole forces between the molecules, whereas tetrachloromethane is non-polar with only the relatively weaker London dispersion forces between the molecules. P.118 # 1,3,5 1. (a) Four unusual properties of water are a high boiling and melting point, low density in the solid state, high surface tension, and high specific heat capacity. (b) Water s high boiling and melting points are due to the strong intermolecular forces of hydrogen bonds. The low density of ice is caused when hydrogen bonds arrange the molecules into a crystalline structure where there is more space between the molecules than there is in liquid water. Water s high surface tension is caused by its hydrogen bonds, which hold water molecules tightly together and cause it to take a shape that has the smallest possible surface area. Water s high specific heat capacity will be explained in future chemistry courses. 3. The molecules in liquid water are closer together and much more jumbled than the molecules in ice. The relatively higher energy of liquid water molecules overcomes the hydrogen bonds resulting in more water molecules per unit volume (hence a greater density). Water molecules in ice, however, are organized in a much more uniform structure (a crystal lattice) because the hydrogen bonds are strong enough to keep the less energetic molecules in place. This results in fewer molecules per unit volume and hence a smaller density. 5. Answers may vary. Sample answer: Examples of ways that life on Earth would be different if water were a non-polar molecule would include effects from the inability of water to form strong hydrogen bonds. Water would not have its high specific heat capacity, so weather systems would be very different. Water would not have high surface tension, so bugs could not stand on water, water could not go up trees, and raindrops would not be the way they are. Ice would not float on liquid water. Lakes would freeze from the bottom up. This would change the potential of lakes as a habitat and allow more evaporation, since water evaporates faster than ice. More water in the atmosphere would contribute to weather changes AW13

14 P.130 # 45,46,54, (a) At room temperature, hydrogen sulfide is a gas, so room temperature must be higher than the boiling point of hydrogen sulfide. Water, on the other hand, is a liquid at room temperature, so its boiling point must lie above room temperature. Thus water has a higher boiling point than hydrogen sulfide. (c) The molecular shapes of H2O and H2S are the same. The bonds are asymmetrically distributed in three dimensions in the same manner for each molecule. (d) The difference in boiling points of water and hydrogen sulfide can be accounted for by the fact that hydrogen bonds can form between water molecules, but not between hydrogen sulfide molecules, giving water a much stronger intermolecular attraction than hydrogen sulfide. The greater degree of intermolecular attraction in water requires more energy to separate the molecules so that it can become a gas. Thus, water has the higher boiling point. 46. It is important to drain water pipes in unoccupied, unheated homes in the winter because, with no heating, the temperatures inside the house could be low enough to freeze the water in the pipes. The expansion of water as it becomes ice could burst the pipes. If temperatures then warm sufficiently, the ice could melt and water could leak out, flooding the home. 54. (a) When a thin stream of decane is passed near a negatively charged vinyl strip, the decane will not be deflected. The electronegativity difference between hydrogen and carbon is 0.4, so the carbon hydrogen bonds in decane are only slightly polar. In addition, the bonds are symmetrically distributed in three dimensions, so decane molecules are non-polar. Decane molecules, therefore, will not be attracted to a charged vinyl strip 61. Adding soap to water affects the ability of water to form beads on a horizontal surface because the soap reduces the surface tension of the water. Water forms beads on a smooth surface because of its strong intermolecular attraction, which is primarily due to hydrogen bonds. This causes water molecules to be attracted to one another rather than to the air above it and thus to form a shape with a minimum surface area. A spherical shape has the least surface area, so beads of water are like little spheres resting on a surface. The forces that form these spheres are strong enough to prevent gravity from flattening them. If soap molecules reduce the strength of the intermolecular forces in water, the water molecules will no longer be able to pull hard enough on one another to form beads. Instead, gravity will pull the water down into a thin layer. REVIEW - BONDING P read over all the questions, attempt as many as possible (write solutions to questions you find challenging). AW14